One of the key advantages of fiber optics is that different wavelength channels traveling in the same fiber have very little interference. This allows the use of wavelength division multiplexed (WDM) systems, in which data is carried by several optical carriers, each having a different wavelength. Each wavelength channel is generated by an independent laser source modulated separately with different data, hence increasing the total amount of data transmitted. These wavelength channels need to be spatially combined into the same fiber. An arrayed waveguide grating (AWG) accomplishes this task.
A system for long-reach lightwave data transmission through optical fibers has been described in U.S. patent application Ser. No. 10/289,944, filed Nov. 6, 2002 by Daniel Mahgerefteh et al. for POWER SOURCE FOR A DISPERSION COMPENSATION FIBER OPTIC SYSTEM, which patent application is hereby incorporated by reference. Azna LLC of Wilmington, Mass. sometimes refers to the transmitter apparatus of this patent application as a Chirp Managed Laser (CML™). In this system, a frequency modulated (FM) source is followed by an optical discriminator, also sometimes referred to as an optical spectrum reshaper (OSR), which converts frequency modulation into a substantially amplitude modulated (AM) signal and partially compensates for the dispersion in the transmission fiber. A number of optical discriminators are described in this patent application, including an arrayed waveguide grating (AWG).
Also, in U.S. patent application Ser. No. 10/615,218, filed Jul. 8, 2003 by Daniel Mahgerefteh et al. for WAVELENGTH DIVISION MULTIPLEXING SOURCE USING MULTIFUNCTIONAL FILTERS, which patent application is hereby incorporated herein by reference, a system is disclosed for combining several chirp managed laser sources into a single optical beam, whereby to achieve wavelength division multiplexing. In this patent application, optical filters function as the multiplexer as well as the optical discriminator responsible for converting the FM modulated signal from the source into the AM signal sent down the fiber.